Zinc Ameliorates Cadmium-Induced Immunotoxicity by Modulating Splenic Immunosuppressive Indoleamine 2,3-Dioxygenase Activity, Hematological Indices, and CD4+ T Cells via Inhibition of Cadmium Uptake in Male Wistar Rats

Cadmium (Cd)-induced immunotoxicity has become a matter of public health concern owing to its prevalence in the environment consequently, great potential for human exposure. Zinc (Zn) has been known to possess antioxidant, anti-inflammatory, and immune-boosting properties. However, the ameliorating influence of Zn against Cd-induced immunotoxicity connecting the IDO pathway is lacking. Adult male Wistar rats were exposed to normal drinking water with no metal contaminants (group 1), group 2 received drinking water containing 200 μg/L of Cd, group 3 received drinking water containing 200 μg/L of Zn, and group 4 received Cd and Zn as above in drinking water for 42 days. Cd exposure alone significantly triggered the splenic oxidative-inflammatory stress, increased activities of immunosuppressive tryptophan 2,3-dioxygenase (TDO), indoleamine 2,3-dioxygenases (IDO) activities/protein expression, and decreased CD4+ T cell count, and a corresponding increase in the serum kynurenine concentration, as well as alterations in the hematological parameters and histologic structure when compared with the control (p < 0.05). Zn alone did not have any effect relative to the control group while co-exposure significantly (p < 0.05) assuaged the Cd-induced alterations in the studied parameters relative to the control. Cd-induced modifications in IDO 1 protein expression, IDO/TDO activities, oxidative-inflammatory stress, hematological parameters/CD4+ T cell, and histological structure in the spleen of rats within the time course of the investigation were prevented by Zn co-exposure via inhibition of Cd uptake.

IDO-1 impairs antitumor immunity of natural killer cells in triple-negative breast cancer via up-regulation of HLA-G

BACKGROUND

Triple-negative breast cancers (TNBC) are highly aggressive malignancies with poor prognosis. As an essential enzyme in the tryptophan-kynurenine metabolic pathway, indoleamine 2,3 dioxygenase-1 (IDO-1) has been reported to facilitate immune escape of various tumors. However, the mechanism underlying the immunosuppressive role of IDO-1 in TNBC remains largely uncharacterized.

METHODS

We examined the IDO-1 expression in 93 clinical TNBC tissues and paired adjacent normal tissues, and analyzed the regulation role of environmental cytokines like IFN-γ in IDO-1 expression. The effect of IDO-1 expression in TNBC cells on the function of NK cells were then evaluated and the underlying mechanisms were exploited.

RESULTS

IDO-1 expressed in 50 of 93 (54.1%) TNBC patients. TNBC patients with high IDO-1 expression tended to have more infiltrated immune cells including NK cells, which are less active than patients with low IDO-1 expression. NK cells could produce IFN-γ, which induced IDO-1 expression in TNBC cells, whereas IDO-1 impaired the cytotoxicity of co-cultured NK cells by upregulation of HLA-G. Blockade of HLA-G improved the antitumor activity of NK cells to TNBC in vivo.

CONCLUSION

TNBC cells induce dysfunction of NK cells through an IFN-γ/IDO-1/HLA-G pathway, which provide novel insights into the mechanisms of TNBC progression and demonstrate the applicability of IDO-1 and HLA-G targeting in the treatment of TNBC.

Indoleamine 2,3-dioxygenase controls fungal loads and immunity in Paracoccidioidomicosis but is more important to susceptible than resistant hosts

Background

Paracoccidioidomycosis, a primary fungal infection restricted to Latin America, is acquired by inhalation of fungal particles. The immunoregulatory mechanisms that control the severe and mild forms of paracoccidioidomycosis are still unclear. Indoleamine 2,3-dioxygenase (IDO), an IFN-γ induced enzyme that catalyzes tryptophan metabolism, can control host-pathogen interaction by inhibiting pathogen growth, T cell immunity and tissue inflammation.

Methodology/Principal Findings

In this study, we investigated the role of IDO in pulmonary paracoccidioidomycosis of susceptible and resistant mice. IDO was blocked by 1-methyl-dl-tryptophan (1MT), and fungal infection studied in vitro and in vivo. Paracoccidioides brasiliensis infection was more severe in 1MT treated than untreated macrophages of resistant and susceptible mice, concurrently with decreased production of kynurenines and IDO mRNA. Similar results were observed in the pulmonary infection. Independent of the host genetic pattern, IDO inhibition reduced fungal clearance but enhanced T cell immunity. The early IDO inhibition resulted in increased differentiation of dendritic and Th17 cells, accompanied by reduced responses of Th1 and Treg cells. Despite these equivalent biological effects, only in susceptible mice the temporary IDO blockade caused sustained fungal growth, increased tissue pathology and mortality rates. In contrast, resistant mice were able to recover the transitory IDO blockade by the late control of fungal burdens without enhanced tissue pathology.

Conclusions/Significance

Our studies demonstrate for the first time that in pulmonary paracoccidioidomycosis, IDO is an important immunoregulatory enzyme that promotes fungal clearance and inhibits T cell immunity and inflammation, with prominent importance to susceptible hosts. In fact, only in the susceptible background IDO inhibition resulted in uncontrolled tissue pathology and mortality rates. Our findings open new perspectives to understand the immunopathology of paracoccidioidomycosis, and suggest that an insufficient IDO activity could be associated with the severe cases of human PCM characterized by inefficient fungal clearance and excessive inflammation.

Immunoprotection to paracoccidiodomycosis, a systemic mycosis endemic in Latin America, is mediated by T cell immunity whereas immunosuppression characterizes the severe forms of the disease. Indoleamine 2,3-dioxygenase (IDO), an enzyme mainly induced by IFN-γ, catabolizes tryptophan along the kynurenines pathway. Tryptophan deficiency has been associated with reduced pathogen growth, while elevated levels of kynurenines with suppressed immune responses. In this study, the role of IDO in pulmonary paracoccidioidomycosis was investigated using resistant and susceptible mice. In both mouse strains, IDO blockade by 1-methyl tryptophan resulted in inefficient fungal clearance accompanied by enhanced T cell immunity. Despite these equivalent biological effects, only in susceptible mice IDO inhibition caused progressive fungal growth and tissue pathology resulting in increased mortality. Our findings demonstrate for the first time that IDO exert a yet unexplored immunoregulatory role in pulmonary paracoccidioidomycosis that can be particularly important in the severe cases of the disease.

Gut inflammation and indoleamine deoxygenase inhibit IL-17 production and promote cytotoxic potential in NKp44+ mucosal NK cells during SIV infection

Natural killer (NK) cells are classically viewed as effector cells that kill virus-infected and neoplastic cells, but recent studies have identified a rare mucosal NK- cell subpopulation secreting the TH17 cytokine IL-22. Here, we report identification of 2 distinct lineages of mucosal NK cells characterized as NKG2A(+)NFIL3(+)RORC(-) and NKp44(+)NFIL3(+)RORC(+). NKG2A(+) NK cells were systemically distributed, cytotoxic, and secreted IFN-γ, whereas NKp44(+) NK cells were mucosae-restricted, noncytotoxic, and produced IL-22 and IL-17. During SIV infection, NKp44(+) NK cells became apoptotic, were depleted, and had an altered functional profile characterized by decreased IL-17 secretion; increased IFN-γ secretion; and, surprisingly, increased potential for cytotoxicity. NKp44(+) NK cells showed no evidence of direct SIV infection; rather, depletion and altered function were associated with SIV-induced up-regulation of inflammatory mediators in the gut, including indoleamine 2,3-dioxygenase 1. Furthermore, treatment of NKp44(+) NK cells with indoleamine 2,3-dioxygenase 1 catabolites in vitro ablated IL-17 production in a dose-dependent manner, whereas other NK-cell functions were unaffected. Thus lentiviral infection both depletes and modifies the functional repertoire of mucosal NK cells involved in the maintenance of gut integrity, a finding that highlights the plasticity of this rare mucosal NK-cell population.

Immature dendritic cells expressing indoleamine 2,3-dioxygenase suppress ovalbumin-induced allergic airway inflammation in mice

BACKGROUND

Proliferation of activated CD4+ T lymphocytes is inhibited by indoleamine 2,3-dioxygenase (IDO).

OBJECTIVE

We undertook the present study to test the hypothesis that IDO-expressing immature DCs (imDCs) can restore immune tolerance in mice suffering from allergic airway inflammation.

METHODS

imDCs were generated from murine bone marrow cells using granulocyte-macrophage colony-stimulating factor.The imDCs were subsequently transfected with an IDO expression vector (pEGFP-N1-IDO). Surface marker expression, including CD11c, MHCII, CD80, and CD86, was analyzed using flow cytometry. IDO-expressing imDCs were injected into the trachea of ovalbumin (OVA)-sensitized mice, and lung histopathology and cytokine expression in bronchoalveolar lavage fluid were assessed. The splenic CD4+ T cells of OVA-sensitized mice were isolated and co-cultured with pEGFP-N1-IDO-expressing imDCs, and apoptosis of CD4+ T cells was detected using the terminal deoxynucleotidyl transferase dUTP nick end labeling assay.

RESULTS

Expression of IDO in imDCs did not alter cell surface molecule expression. We observed marked lung inflammation, elevated total cell and eosinophil count, and altered cytokine levels in OVA-sensitized mice. These parameters improved upon inoculation with IDO-expressing imDCs. Co-culture with IDO-expressing imDCs also induced apoptosis, inhibited IL-4 and IL-5 expression, and upregulated IFN-gamma expression in CD4+ T cells.

CONCLUSIONS

IDO-expressing imDCs induced T(H)2 cell apoptosis and reduced T(H)2 cell activation and allergic airway inflammation in OVA-sensitized mice. Thus, upregulation of IDO expression may provide a novel immunointervention strategy for asthma treatment.

Heme oxygenase-1 inhibits rat and human breast cancer cell proliferation: mutual cross inhibition with indoleamine 2,3-dioxygenase

Heme oxygenase-1 (HO-1) is the rate limiting enzyme of heme catabolism whereas indoleamine 2,3 dioxygenase (IDO) catabolizes tryptophan through the kynurenine pathway. We analyzed the expression and biological effects of these enzymes in rat and human breast cancer cell lines. We show that rat (NMU and 13762) but not human cells (MCF-7 and T47D) express HO-1. When overexpressed, we found this enzyme to have anti-proliferative and proapoptotic effects by antioxidant mechanisms in these four cell lines. We show that IDO is expressed by rat and human breast cancer cells. IDO inhibition with 1-MT and siRNA leads to diminished proliferation in rat cells. In contrast, HO-1 negative human cell lines increase proliferation upon IDO inhibition. Since we also demonstrate that IDO inhibits the anti-proliferative HO-1, we propose that IDO has opposite effects on proliferation depending on the coexpression or not of HO-1. We also describe that HO-1 inhibits IDO at the post-translational level through heme starvation. In vivo, we show that rat normal breast expresses HO-1 and IDO. In contrast, N-nitrosomethylurea-induced breast adenocarcinomas only express IDO. In conclusion, we show that HO-1/IDO cross-regulation modulates apoptosis and proliferation in rat and human breast cancer cells.

Dendritic Cells and CD4+CD25+ T Regulatory Cells: Crosstalk Between Two Professionals in Immunity versus Tolerance

Dendritic cells (DCs) are professional antigen presenting cells (APCs). (CD4+)CD25+ T regulatory cells (T regs) are recognized as professional regulatory cells. DCs not only initiate T cell immunity by uptake, processing and presentation of specific antigens, but also induce immune tolerance by deletion of T cells and/or induction of regulatory T cells. (CD4+)CD25+ T regs maintain immune tolerance by suppressing the function of CD4+ and CD8+ T cells, B cells, macrophages, DCs and NK cells. It would be inconceivable that the delicate balance between immunity and tolerance could be kept impeccable without the crosstalk between DCs and (CD4+)CD25+ T regs. This review focuses on the recent development in our understanding of DCs and (CD4+)CD25+ T regs in immune tolerance, with transforming growth factor-beta (TGF-beta) serving as a potential link between these two professionals.

Indoleamine 2,3-dioxygenase protects corneal endothelial cells from UV mediated damage

Indoleamine-2,3-dioxygenase (IDO) is an intracellular enzyme present in dendritic cells and macrophages. It is a known modulator of T-cell response and contributes to the UV protection of the lens. There yet is no information on IDO activity in the corneal endothelium, protecting the endothelial cells from light mediated damage. We exposed murine corneal endothelial cells (MCEC) with different doses of UV-B light 280-320 nm, probed for IDO mRNA (real-time PCR) and assessed apoptosis rate (flow cytometry) and caspase-3-activity in the cells. The metabolites of the IDO catalysed reaction, l-kynurenine, was also measured. Malondialdehyde was detected for quantification of UV-B-induced oxidative stress. To investigate specificity, IDO effects were blocked by 1-methyl-tryptophan. The effects of IDO overexpression in the MCEC were assessed by transfection of an expression vector. MCEC consistently express IDO at low levels. Exposure to UV-B light led to a dose-responding upregulation of IDO; IDO was found competent converting l-tryptophan into l-kynurenine. Irradiation led to increased apoptosis and caspase-3-activity of MCEC. Supplementation of l-kynurenine or overexpression of IDO in the MCEC could reduce apoptosis significantly following UV-B irradiation. Inhibition of IDO by 1-MT was potent to reverse this effect. IDO and its metabolite l-kynurenine can protect corneal endothelial cells from UV-B-induced oxidative stress and apoptosis. It may be an active protection mechanism against corneal endothelial damage.